Electric heating unit



Feb. 14, 1928. '1,658,990

f A. D. KEENE ELECTRIC HEATING UNI T Filed Maron 2e. 1525" Patented Feb. 14, 1928.

UNITED STATES PATENT OFFICE.

ALVIN D. KEENE, yOF PITTSBURGH, PENNSYLVANIA, ASSIGNOR TO WESTINGI-IOUSE ELECTRIC & MANUFACTURING COMPANY, A CORPORATION 0F PENNSYLVANIA.

ELECTRIC HEATING UNIT.

Application led March 26, 1925. Serial No. 18,425.

My invention relates to electric heatingr devices and particularly to embedded electric heating units.

The object of my invention to provide an electric heating unit. that shall he capable ot'operation at relatively high temperatures without a resistor member embodied therein becoming oxidized.

In practicing my invention, I provide a rcsistor ivire, preferably Wound into an open helix, and cover the same ivith a comminnted electric-insulating material. and then embed the sam-e ina mass of powdered, heataud electric-conducting material that is 'then tightly compressed thereon.

In thesingle sheet of drawings., v

Figure 1 is a top plan vieiv ot an electric heating element embodying my invention,

Fig. 2 is a view. in lateral section therethrough, taken on the line II-II ot Fig. 1.A

Fig. 3 is a fragment-ary enlarged view oi an insulated resistor member comprising` a part of the device embodying` my invention,

Fig. 4 is a` vienT oit av modified form ot dcvice embodying my invention,

Fig. 5 is an end vien7 thereof, and

Fig. 6 is a fragmentary view. in side elevation, of a. further modication ot a heating element embodying'my invention.

An electric heating element, designated generally -by the numeral- 11, comprises a resistor Wire 12 that is preferably Wound to helical form after which the respective turns thereof are spaced apart. It desired, the wire may be Wound With the adjacent turns spaced apart and as this requires a much longer form or mandrel upon which to Wind the Wire, I prefer to effect the spac ing after the coil has been Wound. Any de sired diameter of helix may be employed in accordance with the requirement ot either the Jfurnace or the device, with which the heating element -is to b-e associated, as ivell as in accordance with the amount of resistance Which it is desired that the completed resistor member shall have. A

After the helix has been Wound and the turns spaced, itis dipped into moistened, comminu-ted, electric-insulating material, such as alundum` a suihcient number ot times until a coating, designated by the numeral 13 in Fig. 3, has been formed around and over the entire length of the resistor member 12. While dipping may be employed to eil'ect such coating, any other suitable or desired method that will eiect the desired results may be employed. The coat ing is permitted to dry and the insulated resistor member is then wound on a suitable. former oi any kind desired, that Will hold the helically ivound resistor member in the iinal position ot' the individual parts thereof relatively to each other. Such former may be made of relatively simple form. such as a ivooden plate having pegs therein, around which the helix may be ivound to the form illustrated particularly in Fig. 1 of the draiving.

A mold (not shown) of substantially rectangular contour may have placed therein a quantity ot an initially moistened or comininuted heat-and-electric conducting material` such as carborundum. which material maybe mixed with a. small lquantity. say 5 to 10% ot clay to constitute a binder. The resistor member that has been temporarily placed on the hereinbetore mentioned former is then lightly pressed .into lthe comminuted heat-andelectric-conducting matcrial to an extent suthcient to hold the formed resistor members in their proper operative positions.

It dcsired,or considered necessary, `grooves may be Jformed in the heat-andelectricconducting material placed in the mold and the helically Wound resistor Wire located therein, after ivhich an additional quantity ot heat and-electric-conducting material` is sitted over the resistor mcn'iher which is then tightlv compressed unt-il a slab or plate 1li. is formed. as is illustrated particularly in 1 and 2 ot the drawing. I prefer to employ a relatively high pressure in order that the material may be in intimate heat-comlucting contact with the insulated resistor Wire and that it may have some mechanical strength. Such a plate acts not only as a'heat-conducting material, but also acts as a inutile when a heatingunit ot' this kind is mounted in an oven or in an electric furnace structure.

-A plurality of terminal members 15 and 1.6 that consist of a rod or bar of a highly refractory metal, such -as nichrome, extend into the plate or slab let and the ends ot the resistor Wire 12 are Wrapped therearound a vnumber of times. The terminal members 15 and 1G are held in their proper operative positions relatively to the completed heating unit by 'means provided in the hereinbefore mentioned mold and a layer 17, ot electricinsulating material, such as alundum, may be placed thercaround in order to insulate the terminal members from the electric conducting material comprising the slab 14.

The construction of the terminal members is not further described or claimedin this application, as it forms the subject-matter of my copending application, Serial No. 18,424, filed March 26, 1925 which is assigned to the lVestinghouse Electric & Mfg. Company. I

In. Figs. 4 and 5 is illustrated a modified form of heating element embodying' 'my invention, iu which the resistofiifire is helically Wound and remains in the form of a straight rod. After the Wire has been Wound into helical form and insulated as hereinbefore described (as illustrated in Fig. 3) it lisimbedded in a'quantity. of heat-and-elecvtric conductinu material, such as carborundum, as herei'nlbefore described, but the completed form is that of a rod, as shown particularly in Fig. 4.

To effect s'uch coating, I may employ a suitable process vthat-l employs a mold of the l same general character and operation -ashereinbefore described, dilfering only in that electric-conducting material thatv is made.

the 'material is molded to substantially rod `shape, or I may cause the insulated helix of Wire to, be forced out through a nozzle by pressure applied to a mass of the heat-andsufiiciently plastic to permit of such extrusion. A mass 18 of this material' is located around the outside of the helix and a similar mass 19 is located inside of the helix,'the portion 19 serving to conduct the heat outwardly to the surface of the portion 18.

In Fig. 6, of the drawing, I have illustrated a modified-form which I may employ when an elongated rod form. Ofheater is the interposition of the electric-resisting.

coating 13.

' In the rod form of heating units, any suit- -'-f'-'able or desired type of terminal construction may be employed, as for instance, the resistor wire maybe doubled on itself a number of times or the terminal members 15 land,

16 hereinbefore ldescribed may he employed. The use ot the electric-insulating coating 13 is necessary when va plurality of parallelextending convolutions, such as shown in Fig. 1 of the drawing, are employed, as the voltage drop between the ends of the adjacent convolutions may be high enough to cause a current to iow therebetween and canse a burning out of the heating element.

However, when the rod-form of heating unit is employed, this danger is not present and even if current does traverse the carborundum coating, no particular harm Will be done, as the amountthereof is so low as to cause no burning out of the resistor. This is effected by so proportioning theresistor wire-proper, the spacing between-'the adjacent turns thereof, and by so operating the heating unit that the temperaturel ofthe Since various modiiications and changesmay be made Without departing. from the spiritA and scope of the invention, I desire that only such limitations shall be placed -v thereon as are imposed by the prior art.

I. claim as my invention:

1. The method of making an electric heating element that-comprises the steps of coating a resistor wire, Wound into an open helix, with initially-moistened, powdered electricinsulating material, embedding the same in a mass of initially-moistened, electricconducting material "having high heat-conductivity, compressing said heat-and-electricconducting material around and into said helix andV then heating said element.

2. The method of'making an electric heating element that comprises the steps of coating a resistor Wire, Wound'into 1an open aluminum oxide,'embedding the same in a mass of initially-moistened, powdered silicon carbide, compressing the same and then heating said element.

In testimony whereof, I have hereunto subscribed my name this 13th day of4 March, 1925.

i ALVIN n. KEENE. y

he1ix, with initially-meistened, powdered I 

